Currently, conventional optical fibers used for optical fiber communication systems adopt a structure in which an outer periphery of one core is surrounded by a clad, and information is transmitted on fibers with an optical signal confined in this core. Further, as the optical fiber communication systems spread, the amount of information to be transmitted is dramatically increasing in recent years. Following an increase in the amount of information to be transmitted, the optical fiber communication systems use several tens or several hundreds of multiple optical fibers to perform long-haul optical communication of a large volume.
It is known that, to reduce the number of optical fibers in such an optical fiber communication system, a plurality of signals are transmitted by means of lights propagating in respective cores using a multicore fiber in which outer peripheries of a plurality of cores are surrounded by one clad.
Following Non-Patent Document 1 discloses an example of such a multicore fiber. In this multicore fiber, a plurality of cores are arranged in one clad. Further, to reduce crosstalk between the respective cores, propagation constants of the respective cores are different from each other, and refractive indices of the respective cores are different from each other.
[Patent Document 1] International Publication No. WO2010/038863